In photomechanical processes, a system for forming images which exhibits high contrast photographic characteristics (especially a gamma (.gamma.) value of 10 or more) is required for satisfactory reproduction of continuous tone or line originals by means of dot image.
For this purpose, a general method has so far been employed of using a hydroquinone-containing developing solution in which the effective concentration of sulfite ion is extremely lowered (generally to 0.1 mole/liter or less): this is a so-called infectious developer. However, the developing solution used in such a method is exceptionally unstable, and cannot stably withstand more than three days' storage because of the low sulfite ion concentration therein.
U.S. Pat. No. 2,419,975 describes that a high contrast negative image is obtained by addition of certain hydrazine compounds to a silver halide emulsion, and it requires the use of a developing solution having a high pH value such as 12.8 to provide a high contrast (.gamma..gtoreq.10) negative image by taking advantage of the hydrazine compounds described specifically in that patent specification. However, a strong alkali developer having a pH value near 13 is easily subject to air oxidation and unstable. Therefore, it cannot withstand long term storage and use. Although the keeping quality is, of course, improved by increasing the sulfite ion content, the addition of a large amount of sulfite is required for providing a sufficient improvement in the stability of such a high pH developer, and thereby not only is contamination of processing solutions caused, but also the serious problem of inhibiting the image from acquiring high contrast.
Under these circumstances, an image-forming system which does not have the above-described defects, provides a high contrast image, and ensures excellent keeping quality of processing solutions used therein has been needed.
For the purpose of meeting this need, a system for forming a high contrast negative image having a gamma of more than 10 wherein silver halide photographic materials having emulsions of the kind which form latent image predominantly at the surface of the grains, and in which particular acylhydrazine compounds which are not described in U.S. Pat. No. 2,419,975 as described above are incorporated, are processed with a stable developer having a pH of from 11.0 to 12.3, has been proposed in U.S. Pat. Nos. 4,224,401, 4,168,977, 4,166,742, 4,311,781, 4,272,606, 4,221,857, 4,243,739 and so on.
However, such an image-forming system still has a problem in that a high contrast image is difficult to produce when subjected to a so-called "rapid access processing" (that is, this terminology refers to exceptionally rapid photographic processing, and more specifically, to a processing wherein the total processing time from beginning of processing to the finish thereof at which drying of the processed film is completed is within the range of 90 to 120 seconds, of which the time allotted to development is from 15 to 60 seconds).
On the other hand, silver halide emulsions whose grains are formed in the presence of rhodium salts are described as high contrast ones, e.g., in British Pat. No. 775,197, U.S. Pat. No. 3,531,289, and so on. However, those rhodium salts provide only a minor contribution to the formation of the contrasty image (e.g., according to Example 1 of U.S. Pat. No. 3,531,289, addition of the rhodium salt only increased the contrast from 2.60 to 3.20), and therefore do not enable the formation of such a high contrast image as is required of silver halide photographic materials for photomechanical processes.